B. Marmiroli

Sharp beveled tip hollow microneedle arrays fabricated by LIGA and 3D soft lithography with polyvinyl alcohol

This paper describes a fabrication process of hollow microneedle arrays with a sharp beveled tip for transdermal drug delivery. A master is fabricated through a double deep x-ray lithography process. First, a polymethylmethacrylate (PMMA) sheet is exposed to produce single PMMA parts with a sawtooth profile. The tip angle of each tooth determines the final tip angle of the microneedles. The PMMA parts are assembled and glued on a conductive substrate and then exposed through a second x-ray mask containing an array of hollow triangles as absorbing structures. A metal layer is then electrodeposited around the needles in order to form the future base of the array. A polyvinyl alcohol (PVA) solution is cast on top of the master to form a negative mold of the microneedle array after a low temperature curing and peel-off steps. A liquid PMMA solution is cast on top of the PVA negative mold and after the full PMMA polymerization the PVA is dissolved in water. This fabrication method can be performed in a non-clean room environment and requires little instrumentation. It is therefore compatible with a low-cost mass-fabrication scheme.

Fabrication of 3D micro and nanostructures for MEMS and MOEMS: an approach based on combined lithographies.

X-ray lithography is an established technique for the micro fabrication of MEMS and MOEMS well known for low sidewall surface roughness, submicron critical dimension, and high aspect ratio. Recently the typical characteristics of this technique has been developed approaching new opportunities deriving by the possibility to perform tilted exposure and by the combined use with electron beam lithography that allow to shape with direct patterning already the final material in 3D micro and nanostructures. The general approach is to concentrate the complexity of the multi layer fabrication process required to obtain 3D nanostructures mostly on the lithographic process. This capability represent a micro- and nanofabrication tool enabling new technologies. In this paper will be shown a multiple-tilted X-ray lithography procedure combined with e-beam lithography to create sub-micrometric patterns of arbitrary shape buried in 3D structure. The use of deep x-ray lithography in multi exposure configuration has been also exploited for the production of biodegradable 3D scaffold structures and of micro needles based transdermal delivery tools fabrication.

Bi-propellant Micro-Rocket Engine

Micro-satellites (from 10 kg up to 100 kg) have mass, volume, and electrical power constraints due to their low dimensions. These limitations lead to the lack in currently available active orbit control systems in micro-satellites. Therefore, a micro-propulsion system with a high thrust to mass ratio is required to increase the potential functionality of small satellites. Mechatronic is presently working on a liquid bipropellant micro-rocket engine under contract with ESA (Contract No.16914/NL/Sfe - Microturbomachinery Based Bipropellant System Using MNT). The advances in Mechatronics project are to realise a micro-rocket engine with propellants pressurised by micro-pumps. The energy for driving the pumps would be extracted from a micro-turbine. Cooling channels around the nozzle would be also used in order to maintain the wall material below its maximum operating temperature. A mass budget comparison with more traditional pressure-fed micro-rockets shows a real benefit from this system in terms of mass reduction. In the paper, an overview of the project status in Mechatronic is presented.

Design and Fabrication of Microturbine Rotors for Small Power Generation

TASC/INFM, Sincrotrone Trieste (ELETTRA), and Mechatronic GmbH have started the design of a microturbine powered with compressed gas to be used as an electrical generator in a micro/nanosatellite. The research is funded by ESA for the realization of a liquid bipropellant micro-rocket engine that uses a micro-turbine and micro-pumps in order to pressurize the propellants. The turbine rotors have been fabricated with LIGA technology and die sinking Electro Discharge Machining. LIGA is well adapted to the production of high aspect ratio microstructures with very steep and well polished side walls and it does not limit the choice of material to silicon and derivative but offers the possibility to fabricate the turbine in metallic compounds. Moreover it has been found that LIGA, when coupled with EDM, is an optimum technique to obtain enbloc rotors with small diameter and high aspect ratio blades. The first step of the process is the fabrication of an X-ray mask containing a set of turbine rotors. The mask has been used on the ELETTRA deep X-ray lithography beamline to expose millimeter thick PMMA sheets glued on metallic substrates. After development the substrate is selectively electroplated with copper. The negative tone structures are then used as microelectrodes in a following EDM process. This further step allows obtaining turbines made of every conductive material. In particular we machined

A Transdermal Drug Delivery System Based on LIGA Technology and Soft Lithography

This report presents a transdermal drug delivery system based on LIGA fabricated microparts. It is a portable device combining a magnetically actuated micro gear pump with a microneedle array. The fluidic behaviour of the system is analyzed in order to predict its performance according to the dimension of the microparts and then compared to experimental data. The manufacturing process of both micropump and microneedle array are described.